Field of the Invention
This invention relates to an improvement for the method of manufacturing a semiconductor device and, more specifically, it relates to a method of forming a single crystal film of a semiconductor on a dielectric material and forming a transistor on the film as a substrate.
Description of the Prior Art
For increasing the operation speed of and the density of arranging semiconductor devices, there has been made an attempt for manufacturing a semiconductor integrated circuit with a low stray capacitance by isolating circuit devices with dielectric material, as well as an attempt for laminating the circuit devices vertically and horizontally, that is, manufacturing a so-called three-dimensional circuit device. One of the methods comprises forming a semiconductor layer on a dielectric material and constituting circuit devices in the semiconductor crystalline layer. Such a semiconductor crystalline layer can be formed by depositing a polycrystalline or amorphous semiconductor layer on the dielectric material and irradiating energy rays such as laser beams or electron beams to the surface thereby heating only the surface layer.
Referring to FIGS. 2a and 2b, there are shown a composite body of a semiconductor crystalline layer formed on a dielectric substrate in accordance with the conventional method. In FIGS. 2a and 2b, there are shown a single crystal silicon substrate 11, a silicon oxide film 12, a polycrystalline silicon film 13 and a silicon nitride film 14 deposited on the polycrystalline silicon film 13 and patterned as parallel stripes each of 5 .mu.m width and arranged at 10 .mu.m intervals. The silicon oxide film 12 is formed by a thermal oxidation process, and the polycrystalline silicon film 13 and the silicon nitride film 14 are formed by a chemical vapor deposition process (hereinafter simply referred to as a "CVD" process). The polycrystalline silicon film 13 can be melted and recrystallized, for example, by irradiating argon laser beams restricted to 100 .mu.m diameter in parallel with the stripes of the silicon nitride film 14 at a scanning rate of 25 cm/sec. In this case, since the silicon nitride film 14 serves as a reflection-preventive film for the argon laser beams, the temperature of the polycrystalline silicon film 13 under the silicon nitride film 14 is kept higher than that of the polycrystalline silicon film 13 at the regions where the silicon nitride film 14 is absent. The solidification and recrystallization of the polycrystalline silicon film 13 occurs continuously from the lower temperature region with no silicon nitride film 14 and the regions of the polycrystalline silicon film 13 put between each of the stripes of the silicon nitride film 14 is converted into single crystals.
In the conventional method of irradiating laser beams to the semiconductor layer on the dielectric material for conversion into single crystals, since the silicon nitride film is in direct contact on the polycrystalline silicon, nitrogen atoms in the silicon nitride film intrude into the polycrystalline silicon upon recrystallization to worsen the crystallinity of silicon. Further, if a silicon oxide film is used as a reflection-preventive film, unevenness results to the surface of silicon after recrystallization although the intrusion of impurities into the polycrystalline silicon can be prevented.